The Olive (Olea europaea) is a species of a small tree in the family Oleaceae, native to the coastal areas of the eastern Mediterranean Basin, from Lebanon, Syria and the maritime parts of Turkey and northern Iran at the south end of the Caspian Sea. Its fruit, the olive, is of major agricultural importance in the Mediterranean region as the source of olive oil.

Description

The olive tree is an evergreen tree or shrub native to the Mediterranean, Asia and parts of Africa. It is short and squat, and rarely exceeds 8–15 meters in height. The silvery green leaves are oblong in shape, measuring 4–10 cm long and 1–3 cm wide. The trunk is typically gnarled and twisted.

The small white flowers, with ten-cleft calyx and corolla, two stamens and bifid stigma, are borne generally on the last year’s wood, in racemes springing from the axils of the leaves.

The fruit is a small drupe 1–2.5 cm long, thinner-fleshed and smaller in wild plants than in orchard cultivars. Olives are harvested at the green stage or left to ripen to a rich purple colour (black olive). Canned black olives may contain chemicals that turn them black artificially.

Cultivation And Uses

A selection of olives in a market in Tel Aviv, IsraelThe olive tree has been cultivated since ancient times as a source of olive oil, fine wood, olive leaf, and olives for consumption. The naturally bitter fruit is typically subjected to fermentation or cured with lye or brine to make it more palatable.

Green olives and black olives are washed thoroughly in water to remove oleuropein, a bitter carbohydrate. Sometimes they are also soaked in a solution of food grade sodium hydroxide in order to accelerate the process.

Green olives are allowed to ferment before being packed in a brine solution. American black (“California”) olives are not fermented, which is why they taste milder than green olives.

It is not known when olives were first cultivated for harvest. Among the earliest evidence for the domestication of olives comes from the Chalcolithic Period archaeological site of Teleilat Ghassul in what is today modern Jordan.

Farmers in ancient times believed olive trees would not grow well if planted more than a short distance from the sea; Theophrastus gives 300 stadia (55.6 km) as the limit. Modern experience does not always confirm this, and, though showing a preference for the coast, it has long been grown further inland in some areas with suitable climates, particularly in the southwestern Mediterranean (Iberia, northwest Africa) where winters are mild.

Olive plantation in Andalucia, SpainOlives are now cultivated in many regions of the world with Mediterranean climates, such as South Africa, Chile, Australia, the Mediterranean Basin, Israel, Palestinian Territories and California and in areas with temperate climates such as New Zealand, under irrigation in the Cuyo region in Argentina which has a desert climate. They are also grown in the Córdoba Province, Argentina, which has a temperate climate with rainy summers and dry winters (Cwa). The climate in Argentina changes the external characteristics of the plant but the fruit keeps its original characteristics.

Considerable research supports the health-giving benefits of consuming olives, olive leaf and olive oil (see external links below for research results). The olive tree provides leaves, fruit and oil. Olive leaves are used in medicinal teas.

Olives are now being looked at for use as a renewable energy source, using waste produced from the olive plants as an energy source that produces 2.5 times the energy generated by burning the same amount of wood. The smoke released has no negative impact on neighbors or the environment, and the ash left in the stove can be used for fertilizing gardens and plants. The process has been patented in the Middle East and the US.

Growth And Propagation

Olive trees show a marked preference for calcareous soils, flourishing best on limestone slopes and crags, and coastal climate conditions. They tolerate drought well, thanks to their sturdy and extensive root system. Olive trees can be exceptionally long-lived, up to several centuries, and can remain productive for as long, provided they are pruned correctly and regularly.

The olive tree grows very slowly, but over many years the trunk can attain a considerable diameter. A. P. de Candolle recorded one exceeding 10 m in girth. The trees rarely exceed 15 m in height, and are generally confined to much more limited dimensions by frequent pruning. The yellow or light greenish-brown wood is often finely veined with a darker tint; being very hard and close-grained, it is valued by woodworkers.

The olive is propagated in various ways, but cuttings or layers are generally preferred; the tree roots easily in favourable soil and throws up suckers from the stump when cut down. However, yields from trees grown from suckers or seeds are poor; it must be budded or grafted onto other specimens to do well (Lewington and Parker, 114). Branches of various thickness cut into lengths of about 1 m and planted deeply in manured ground, soon vegetate. Shorter pieces are sometimes laid horizontally in shallow trenches and, when covered with a few centimetres of soil, rapidly throw up sucker-like shoots. In Greece, grafting the cultivated tree on the wild form is a common practice. In Italy, embryonic buds, which form small swellings on the stems, are carefully excised and planted beneath the surface, where they grow readily, their buds soon forming a vigorous shoot.

Occasionally the larger boughs are marched, and young trees thus soon obtained. The olive is also sometimes raised from seed, the oily pericarp being first softened by slight rotting, or soaking in hot water or in an alkaline solution, to facilitate germination.

Where the olive is carefully cultivated, as in Languedoc and Provence, the trees are regularly pruned. The pruning preserves the flower-bearing shoots of the preceding year, while keeping the tree low enough to allow the easy gathering of the fruit. The spaces between the trees are regularly fertilized. The crop from old trees is sometimes enormous, but they seldom bear well two years in succession, and in many instances a large harvest can only be reckoned upon every sixth or seventh season.

A calcareous soil, however dry or poor, seems best adapted to its healthy development, though the tree will grow in any light soil, and even on clay if well drained; but, as remarked by Pliny, the plant is more liable to disease on rich soils, and the oil is inferior to the produce of the poorer and more rocky ground.

In general, a temperature below 14 °F (-10 °C) may cause considerable injury to a mature tree, but (with the exception of juvenile trees) a temperature of 16 °F (-9 °C) will normally cause no harm.

Harvest And Processing

Olives are harvested in the fall. More specifically, green olives are picked at the end of September to about the middle of November. Blond olives are picked from the middle of October to the end of November and Black olives are collected from the middle of November to the end of January or early February. Some Italian and Greek olives are harvested by hand, as the terrain can be mountainous which inhibits harvesting by machine. As a result, the fruit is not bruised which leads to a superior finished product. Furthermore, the fact that branches are sawn off as part of the method of hand harvesting ensures the health of the tree for future production.

Most olives today are harvested by shaking the boughs or the whole tree. Another method involves standing on a ladder and “milking” the olives into a sack tied around the harvester’s waist. Using olives found lying on the ground can result in poor quality oil.

In southern Europe the olive harvest is in winter, continuing for several weeks, but the time varies in each country, and also with the season and the kinds cultivated. A device called the oli-net wraps around the trunk of the tree and opens to form an umbrella-like catcher; workers can then harvest the fruit without the weight of the load around their neck. Another device, the oliviera, is an electric tool that connects to a battery. The oliviera has large tongs that are spun around quickly, removing fruit from the tree. This method is used for olives used for oil. Table olive varieties are more difficult to harvest, as workers must take care not to damage the fruit; baskets that hang around the worker’s neck are used.

The amount of oil contained in the fruit differs greatly in the various cultivars; the pericarp is usually 60–70% oil. Typical yields are 1.5-2.2 kg of oil per tree per year.

Traditional Fermentation And Curing

With one exception (Thassos Olives), olives are inedible when picked from the tree. This is due to the glucoside in their flesh, which makes them taste extremely bitter. To remove this glucoside and render the olive edible, the fruit must be cured.

Olives freshly picked from the tree contain phenolic compounds and oleuropein, a glycoside which makes the fruit unpalatable for immediate consumption. There are many ways of processing olives for table use. Traditional methods use the natural microflora on the fruit and procedures which select for those that bring about fermentation of the fruit. This fermentation leads to three important outcomes: the leaching out and breakdown of oleuropein and phenolic compounds; the creation of lactic acid, which is a natural preservative; and a complex of flavoursome fermentation products. The result is a product which will store with or without refrigeration.

One basic fermentation method is to get food grade containers, which may include plastic containers from companies which trade in olives and preserved vine leaves. Many bakeries also recycle food grade plastic containers which are well sized for olive fermentation; they are 10 to 20 litres in capacity. Freshly picked olives are often sold at markets in 10 kg trays. Olives should be selected for their firmness if green and general good condition. Olives can be used green, ripe green (which is a yellower shade of green, or green with hints of colour), through to full purple black ripeness. The olives are soaked in water to wash them, and drained. 7 litres (which is 7 kg) of room temperature water is added to the fermentation container, and 800 g of sea salt, and one cup (300 g) of white vinegar (white wine or cider vinegar). The salt is dissolved to create a 10% solution (the 800 g of salt is in an 8 kg mixture of salt and water and vinegar). Each olive is given a single deep slit with a small knife (if small), or up to three slits per fruit (if large, e.g., 60 fruit per kg). If 10 kg of olives are added to the 10% salt solution, the ultimate salinity after some weeks will be around 5 to 6% once the water in the olives moves into solution and the salt moves into the olives. The olives are weighed down with an inert object such as a plate so they are fully immersed and lightly sealed in their container. The light sealing is to allow the gases of fermentation to escape. It is also possible to make a plastic bag partially filled with water, and lay this over the top as a venting lid which also provides a good seal. The exclusion of oxygen is useful but not as critical as when grapes are fermented to produce wine. The olives can be tasted at any time as the bitter compounds are not poisonous, and oleuropein is a useful antioxidant in the human diet.

The olives are edible within 2 weeks to a month, but can be left to cure for up to three months. Green olives will usually be firmer in texture after curing than black olives.

There are several methods via which olives can be cured: lye-curing, salt-curing, brine-curing and fresh water-curing. Lye-curing, an unnatural method, is the one resulting in the worst taste as it leeches much of the fruits’ flavor. Salt-curing (also known as dry-curing) involves packing the olives in plain salt for minimum of a month, which produces a salty and wrinkled olive. Olives are placed in a water and salt solution for a few days or more as a part of the of brine-curing process. Fresh-water curing involves soaking the olives in a succession of baths, of which the water is changed daily.

Olives can be flavoured by soaking them in various marinades, or removing the pit and stuffing them. Herbs, spices, olive oil, feta, capsicum (pimento), chili, lemon zest, lemon juice, garlic cloves, wine, vinegar, juniper berries, and anchovies are popular flavourings. Sometimes the olives are lightly cracked with a hammer or a stone to trigger fermentation. This method of curing adds a slightly bitter taste.

Recipes:

Olives are basically used in Pizza toppings, pastas, salads or sandwiches and burgers. So in Ayesha’s Kitchen a huge number of recipes are given which contains mushrooms: